Nanoparticles in general, and nanowires in particular, have been the subject of considerable research in the materials sciences. Part of this interest stems from the fact that nanowires of many materials frequently exhibit properties that are dramatically different from the corresponding bulk materials.
By way of example, germanium (Ge), like nearly all known ceramics, is a brittle material1, and only exhibits measurable ductility2 at high temperatures (greater than 350° C.). These properties result from the directional, covalent bonding between germanium atoms in the crystalline lattice, which blocks the nucleation and movement of dislocations necessary for plastic deformation (the Peierls force). Therefore, unless the temperature is very high, a bulk crystal of Ge fractures when it is deformed just past its yield point.3 Ge also tends to be relatively fragile, with room temperature fracture strengths of only 40 to 95 MPa. These fracture strengths are orders of magnitude less than the ideal strength expected for a perfect Ge crystal of 14-20 GPa,4, 5 and are attributable to the fact that Ge crystals have a variety of nearly unavoidable defects and stresses that serve as sources for crack formation and propagation.
In contrast to bulk Ge, crystalline nanowires of Ge, like those of many other semiconductors, are mechanically flexible due to their nanoscale dimensions. These nanowires are also too small to support defect concentrations similar to bulk materials, and are therefore extremely strong. In fact, the strength of Ge nanowires is close to the ideal strength of a perfect Ge crystal.